These data records may be used to input a linear hydrostatic stiffness matrix. If the matrix has been read from the backing file, the LSTF data record will replace (i.e. overwrite) the existing values within that matrix. If you wish to add TO the existing values, use the ASTF data record (The ASTF Data Record - Additional Hydrostatic Stiffness Matrix).
Note:
This data record is ignored if there is any internal tank associated with this structure.
LSTF data records must be used to define the whole hydrostatic stiffness matrix for a particular structure. If any LSTF data records are used, undefined rows will be re-set to zero.
The Z coordinate of the center of gravity and the buoyancy force at equilibrium must always be defined when using LSTF data records to specify the stiffness matrix.
See the notes at the end of this section about the effects of the LSTF data record on the calculations.
2 5 7 11 16 21 31 41
- --- -- ---- ----- ----- --------- --------- ------
|X| | |LSTF|XXXXX| | | | ...
- --- -- ---- ----- ----- --------- --------- ------
| | | | | | |
| | | | |----------------------
| | | | |
| | | | |_(2)-(7)6 Stiffness Values
| | | | (6E10.0)(Units for freedoms
| | | | 1-3 = force/length,
| | | | 4-6 = force*length/RADIAN)
| | | |
| | | |_(1)Row Number of Stiffness Matrix(I5)
| | |
| | |_Compulsory Data Record Keyword(A4)
| |
| |_Optional User Identifier(A2)
|
|_Compulsory END on Last data record in data category(A3)
(1) This number indicates which row of the stiffness matrix the values input in columns 21-80 relate to.
(2)-(7) These are the values which replace the row (1) in the hydrostatic stiffness matrix.
Note:
Stiffness related forces acting on the structure
The linear hydrostatic stiffness matrix relates to the hydrostatic forces contributing to the equations of static equilibrium of a structure. Specifically, the net linear hydrostatic forces F(s), acting at the center of gravity of a structure, when the structure is at an arbitrary position X, is given by:
F(s) = K ( X(e) - X ) + B(e)
where
K = stiffness matrix
X(e) = equilibrium position
B(e) = buoyancy force at equilibrium
At equilibrium, all forces act in the Z direction of the Fixed Reference Axis (FRA), where X(e)=X, and B(e) = F(s). Thus, the Z coordinate of the center of gravity and the buoyancy force at equilibrium must always be defined, when using the LSTF data record to specify the stiffness matrix, in order to fully describe the hydrostatic forces acting on the structure. These parameters must be input using the ZCGE and BFEQ data records which are described in The ZCGE Data Record - Z Coordinate of the Center of Gravity at Equilibrium and The BFEQ Data Record - Buoyancy Force at Equilibrium.
Effect of the LSTF data record when running Aqwa-Line
Normally Aqwa-Line calculates the hydrostatic stiffness matrix from the element description in Data Category 2. Input of 1 or more LSTF data records indicates that this calculation is to be omitted for the specified structure, and the hydrostatic stiffness matrix will use the specified values. Data Records must be used in sets of 6 to define the full hydrostatic stiffness matrix; undefined values will default to zero.
The hydrostatic stiffness matrix is used in the calculation of the 2nd order drift coefficients. For this purpose it should only represent the hydrostatic stiffness of the outer wetted hull itself; LSTF should not be increased to add in the effect of (e.g.) moorings.